Navigation system

1. A navigation system, comprising: a receiving section that receives traffic information including congestion information; a congestion information acquisition section that obtains from the traffic information, items of congestion information related to a map information display; a congestion information extraction section that extracts, from the items of congestion information obtained by the congestion information acquisition section, a congestion information group with a specified congestion level; an overlap determination area creation section that, based on road links related to the items of congestion information within the congestion information group, creates an overlap determination area that extends both transversely and longitudinally for a specified distance from the road link; a grouping section that groups the items of congestion information having overlapping determination areas; an equal congestion level area creation section that creates an equal congestion level area by connecting the overlapping determination areas of the grouped items of congestion information; and a display control section that displays the equal congestion level area superimposed on the map information display.

2. The navigation system according to claim 1 , wherein the congestion information extraction section extracts the congestion information groups for a plurality of different congestion levels in sequence; the equal congestion level area creation section creates a plurality of different equal congestion level areas that respectively correspond to the congestion information groups extracted by the congestion information extraction section; and the display control section displays the plurality of equal congestion level areas superimposed on the map information display such that the different equal congestion level areas can be distinguished from one another.

3. The navigation system according to claim 2 , wherein the display control section displays mutually differentiated display colors for the plurality of types of the equal congestion level areas superimposed on the map information.

4. The navigation system according to claim 1 , wherein the equal congestion level area creation section comprises: a virtual link creation section that, where the road links have overlap determination areas which do not overlap and are directly connected in a road network, creates a virtual link that joins the road links; and a joining overlap determination area creation section that, based on the virtual link, creates a joining overlap determination area that extends both transversely and longitudinally for a specified distance from the virtual link; and wherein the equal congestion level area creation section creates an equal congestion level area by joining the joining overlap determination area with the overlap determination areas that overlap the joining overlap determination area.

5. The navigation system according to claim 2 , wherein the equal congestion level area creation section comprises: a virtual link creation section that, where the road links have overlap determination areas which do not overlap and are directly connected in a road network, creates a virtual link that joins the road links; and a joining overlap determination area creation section that, based on the virtual link, creates a joining overlap determination area that extends both transversely and longitudinally for a specified distance from the virtual link; and wherein the equal congestion level area creation section creates an equal congestion level area by joining the joining overlap determination area with the overlap determination areas that overlap the joining overlap determination area.

6. The navigation system according to claim 3 , wherein the equal congestion level area creation section comprises: a virtual link creation section that, where the road links have overlap determination areas which do not overlap and are directly connected in a road network, creates a virtual link that joins the road links; and a joining overlap determination area creation section that, based on the virtual link, creates a joining overlap determination area that extends both transversely and longitudinally for a specified distance from the virtual link; and wherein the equal congestion level area creation section creates an equal congestion level area by joining the joining overlap determination area with the overlap determination areas that overlap the joining overlap determination area.

7. The navigation system according to claim 1 , wherein the display control section, when the map information display is reduced to a scale predetermined for a wide area display, superimposes the equal congestion level area on the map information display.

8. The navigation system according to claim 2 , wherein the display control section, when the map information display is reduced to a scale predetermined for a wide area display, superimposes the equal congestion level area on the map information display.

9. The navigation system according to claim 3 , wherein the display control section, when the map information display is reduced to a scale predetermined for a wide area display, superimposes the equal congestion level area on the map information display.

10. The navigation system according to claim 4 , wherein the display control section, when the map information display is reduced to a scale predetermined for a wide area display, superimposes the equal congestion level area on the map information display.